1. Field of the Invention
The present invention relates to an oil-coating roller for applying a releasing oil to a surface of a fixing roller of electrostatic copying machines, electronic cameras, printers, and so forth.
2. Background Art
Conventionally, in electrostatic copying machines, electronic cameras, printers, or the like, the fixing roller of the fixing unit is kept coated with a releasing oil by an oil-applying member such as an oil-coating roller for prevention of toner sticking or paper sheet winding, or prevention of the abrasion of the heating roller. The oil-coating roller is usually constituted mainly of a central core, an oil-retaining layer, and an oil-coating control layer constituted of a porous PTFE film or the like, as necessary. The oil is impregnated and retained in the oil-retaining layer, and is transferred onto the surface of the fixing roller at a required rate.
The oil-coating rollers are used usually as disposable consumables, and are disposed after the oil impregnated in the oil-retaining layer has been used up or the oil has come not to exude at a required rate out of the surface of the porous layer. Therefore, the effective service life of the oil-coating roller is evaluated by the quantity of the oil which can exude out from the oil-retaining layer at a required rate, namely the available oil quantity. In other words, the larger the oil retaining quantity and the smaller the unavailable remaining oil quantity, the longer is the service life of the oil-coating roller.
However, in the case where the oil is impregnated in a larger quantity, the oil tends to leak out from the end face of the oil-retaining layer, although the oil-coating control layer outside the oil-retaining layer prevents the oil leakage from the roller surface. Therefore, in most instances, the roller end faces should be treated for sealing to retard or prevent the oil leakage. This is disadvantageous economically for use as disposable consumables. On the other hand, the decrease of the oil impregnation amount decreases the aforementioned available oil amount to shorten the effective service life.
The oil-retaining layers are known in which sheets of rock wool or sheets of mixed fiber such as aramid or polyester wound in layers, for example, as shown in Japanese Patent Application Laid-Open Nos. 6-348166 and 9-185285. The oil-retaining layer made from such a material has high oil-retaining power, being less liable to cause oil leakage in vertical placement or in practical use. However, such an oil-retaining layer has a low oil impregnation capacity owing to less porosity, and the oil exudation rate can decrease below the required rate even with the oil remaining therein, resulting in a small available oil quantity and a low oil availability ratio, disadvantageously.
Japanese Patent Application Laid-Open Nos. 4-139477 and 2001-318553 discloses an oil-retaining layer constituted of a silicone rubber or a melamine resin sponge. The oil-retaining layer made of such a material is capable of impregnating a larger quantity of oil and exhibits a higher oil availability and a higher available oil ratio owing to high porosity of the material. However, the oil-coating roller employing such a material has a low oil-retaining power to cause oil leakage in vertical placement state or in practical use. Therefore, such a type of oil roller requires a countermeasure against the oil leakage such as sealing at the both end faces for retardation or prevention of the oil leakage. This results in a higher cost of the oil-retaining roller.
As described above, the oil-coating roller is not readily obtainable which is free from oil leakage and simultaneously achieves a large available oil quantity and a high oil availability ratio. The present invention is made to solve the above problem. The present invention intends to provide an oil-coating roller constituted mainly of an oil-retaining layer around a central core, and an oil-coating control layer surrounding the oil-retaining layer, the roller not requiring treatment for sealing the and faces against oil leakage and having a long service life.